The present invention relates to a method and a device for measuring electric currents in n conductors where n is a natural number and n.gtoreq.2.
It is generally known to measure electric currents using a magnetoresistive sensor, in which the output signal is proportional to an electric current to be measured, as described in DE-PS 43 00 605 C2. The magnetoresistive sensor can be used to carry out a potential-free measurement of the current strength of an electric current such that the magnetic field caused by the electric current and the magnetic field gradients are measured with the sensor.
When polyphase currents are to be measured, Hall transducers are used. The disadvantage of Hall transducers is that, due to the physically prescribed magnetic field sensitivity of the Hall elements, an iron core (laminated cores or ferrites) has to be used to guide the flux and concentrate the field. This results in a relatively large overall volume which is an obstacle for integration of the device into planar design technology, such as hybrid circuits. In addition, the Hall elements have to be mounted in an air gap in the flux concentrator, which increases the expenditure for maintaining the air gaps and creepage paths, if the measuring conductor cannot be adequately insulated with respect to the iron core.
According to another known technique described in EP 597 404 A2, operations are carried out with fewer sensors than the number of currents to be determined. For example, the currents of a three-conductor system are sensed with two sensors. According to this technique, it is not the individual magnetic field of the electric conductor which is used for measurement purposes (page 2, lines 50 to 52) but rather the total magnetic field which is produced in a multiconductor system through superimposition of the individual magnetic fields. Determining the field strengths by means of vectors requires the angles of the arrangement to be known. As a result, a complex calculation is necessary which is undesirable.
Furthermore, in the known technique there is a need for sensors which supply an electrical measurement signal which is proportional to the vectorial magnetic field strength.